This invention relates to a fluid powered stepping motor for connecting between a pipe string and a downhole assembly to rotate the downhole assembly relative to the pipe string by raising and lowering the pressure in the pipe string.
This invention has utility when located in any type of pipe string for rotating a downhole tool relative to the tubing string, but it is particularly useful for rotating a downhole tool relative to a string of coil tubing.
More and more wells are being worked over using coil tubing including the drilling of directionally controlled lateral drain holes. The tubing usually extends downwardly through the production tubing that is already in place in the well. The downhole drilling assembly includes a steering tool for indicating at the surface the inclination and direction of the drain hole and a downhole motor for rotating the drill bit. The steering tool, however, must be rotated from time to time to maintain the proper orientation of the tool with the magnetic field of the earth and coil tubing cannot be rotated.